Hi!

I have a phone (Mitel 6930) that does not send an Expire-header but "expire" in Contact during REGISTER:

Session Initiation Protocol (REGISTER)
    Request-Line: REGISTER sip:pbx.example.com SIP/2.0
    Message Header
        Via: SIP/2.0/TLS 192.168.6.16:5061;branch=xxxxxxxxxxxxxxxx;rport
        Route: <sip:pbx.example.com;lr=lr;transport=tls>
        Max-Forwards: 70
        From: "Example" <sip:121212_6666@pbx.example.com>;tag=b0cec92c3e
        To: "Example" <sip:121212_6666@pbx.example.com>
        Call-ID: aaaaaaaaaaaaaaaaa
        CSeq: 1190442896 REGISTER
        Accept-Language: de
        Allow: INVITE, ACK, CANCEL, BYE, NOTIFY, REFER, OPTIONS, UPDATE, PRACK, SUBSCRIBE, INFO, PUBLISH
        Allow-Events: talk, hold, conference, LocalModeStatus
        Contact: "Example" <sip:121212_6666@192.0.2.1:62336>;+sip.instance="<urn:uuid:00000000-0000-1000-8000-08000FB888F5>";expires=300
        Supported: path, gruu
        User-Agent: Mitel 6930/5.0.0.2041
        Aastra-Line: 1
        Aastra-Mac: AAAAAAAAAAAA
        Content-Length: 0

This results in successful register, kamailio forwards REGISTER to asterisk (endpoint registered) and immediatly kamailio sends a new REGISTER with Expire set to 0 to asterisk:

Session Initiation Protocol (REGISTER)
    Request-Line: REGISTER sip:192.168.99.112:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 192.168.99.111:5060;branch=z9hG4bK9f9e.599cf243000000000000000000000000.0
        To: <sip:121212_6666@192.168.99.112>
        From: <sip:121212_6666@192.168.99.112>;tag=7e4f6993bfbf831f6b016fea6683cdca-b98a
        CSeq: 10 REGISTER
        Call-ID: 2bc5fd1061b31723-1350@192.168.99.111
        Max-Forwards: 70
        Content-Length: 0
        User-Agent: kamailio (5.1.6 (x86_64/linux))
        Contact: <sip:121212_6666@192.168.99.111:5060>
        Expires: 0

The phone is then unregistered - the phone also shows "no service". It looks like Kamailio generates this message on it's own (and I don't know why).

I am still learning to implement kamailio as proxy. Reading the docs, I would expect Kamailio to automatically eval the correct parameter:
If the processed message contains neither Expires HFs nor expires contact parameters, this value will be used for newly created usrloc records.  
[1]

What did I miss?
Phones which use the Expire-header are working fine.

Kind regards
Kevin